Wireless Device, Network Nodes and Methods Therein for Handling a Device-to-Device (D2D) Communication during Handover in a Wireless Telecommunications Network

ABSTRACT

A method performed by a first wireless device for handling a device-to-device (D2D) communication with a second wireless device during handover of the first wireless device from a source network node to a target network node in a wireless telecommunications network is provided. The first wireless device interrupts the D2D communication. Then, the firs wireless device determines a first uplink timing difference as the difference between the uplink timing to the source network node and the uplink timing to the target network node. Further, the first wireless device reconfigures the D2D communication based on the first uplink timing difference. Then, the first wireless device rest&#39;s the D2D communication as reconfigured. A first wireless device is also provided, along with a target network node, a source network node and methods therein for handling a D2D communication.

RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/408,504, filed 16 Dec. 2014, which is a national stage entryunder 35 U.S.C. §371 of international patent application serial no.PCT/SE2013/050553 filed 16 May 2013. The entire contents of each of theaforementioned applications is incorporated herein by reference.

TECHNICAL FIELD

Embodiments herein relate to Device-to-Device (D2D) communications in awireless telecommunications network. In particular, embodiments hereinrelate to handling a D2D-communication during handover of a wirelessdevice in a wireless telecommunications network.

BACKGROUND

In wireless communication networks, recent developments of the 3GPP LongTerm Evolution, LTE, facilitate accessing local IP based services in thehome, the office, in public hot spot or even in outdoor environments.One area in which the access and local connectivity of these local IPbased services may be used is in the direct communication betweenwireless devices in the close proximity of each other. In this case,close proximity may typically refer to less than a few tens of meters,but sometimes even up to a few hundred meters.

This direct mode or Device-to-Device, D2D, communication may demonstratea number of potential gains over traditional cellular communication.This is because D2D devices are much closer to one another than othercellular devices that have to communicate via a cellular access point,e.g. a radio network node such as an eNodeB.

However, it should be noted that it is preferable to maintain thecontrol of the D2D communication from a network point of view in orderto ensure an efficient use of resources and interference handling.

In these mixed cellular and D2D wireless communication networks, it hasbeen suggested to locate D2D communication on cellular uplink, UL,resources in a way such that Time-Division Duplex, TDD, is the duplextransmission scheme of the D2D communication. This means that thecellular UL resources would be allocated for D2D communicationtransmission in both upstream and downstream directions between each D2Dpair of wireless devices in a Time-Division Multiplexed, TDM, manner.

Once the wireless devices discover the proximity of each other, thewireless devices and/or the network may initiate the establishment ofthe D2D link between the two wireless devices. This is commonly referredto as D2D bearer establishment, and will not be discussed furtherherein.

However, upon having established the D2D link between the two wirelessdevices, there is a problem of how to handle the D2D communication whenone of the wireless devices is moving out of the cellular coverage ofits current cell and into the cellular coverage of another cell, i.e.during a handover. Thus, there is a need to provide way of handling aD2D communication during handover of wireless device in a wirelesscommunications network.

WO2011/109027 A1 describes a handover of a D2D pair of wireless devicesbetween different cells. However, in this case, both of the wirelessdevices of the D2D pair are part of the handover and the network controlo the D2D communication may simply pass from network node of the sourcecell to the network node of the target cell.

SUMMARY

It is an object of embodiments herein to provide way of handling a D2Dcommunication during handover of wireless device in a wirelesscommunications network.

According to a first aspect of embodiments herein, the object isachieved by a method performed by a first wireless device for handling adevice-to-device, D2D, communication with a second wireless deviceduring handover of the first wireless device from a source network nodetarget network node in a wireless telecommunications network. The firstwireless device interrupts the D2D communication. Then, the firstwireless device determines a first uplink timing difference as thedifference between the uplink timing to the source network node and theuplink timing to the target network node. Further, the first wirelessdevice reconfigures the D2D communication based on the first uplinktiming difference. Then, the first wireless device restarts the D2Dcommunication as reconfigured.

According to a second aspect of embodiments herein, the object isachieved by a first wireless device for handling a D2D communicationwith a second wireless device during handover of the first wirelessdevice from a source network node to a target network node in a wirelesstelecommunications network. The first wireless device comprisesprocessing circuitry configured to first interrupt the D2Dcommunication. The processing circuitry is configured to then determinea first uplink timing difference as the difference between the uplinktinning the source network node and the uplink tinning to the tan-letnetwork node. Further, the processing circuitry is configured toreconfigure the D2D communication based on the first uplink tinningdifference, and restart the D2D communication as reconfigured.

According to a third aspect of embodiments herein, the object isachieved by a method performed by a target network node for handling aD2D communication between a first wireless device and a second wirelessdevice during handling of the first wireless device to the targetnetwork node from a source network node in a wireless telecommunicationsnetwork. The target network node, after completing the handover,receives at least a first uplink timing difference of the first wirelessdevice from the first wireless device. Also, the target network nodedetermines a scheduling scheme for the D2D communication based on atleast the first uplink timing difference of the first wireless device,which first uplink timing difference is the difference between theuplink timing of the first wireless device to the source network nodeand the uplink timing of the first wireless device to the target networknode.

According to a fourth aspect of embodiments herein, the object isachieved by a target network node for handling a D2D communicationbetween a first wireless device and a second wireless device duringhandover of the first wireless device to the target network node from asource network node in a wireless telecommunications network. The targetnetwork node comprises processing circuitry configured to, aftercompleting the handover, receive at least a first uplink timingdifference of the first wireless device from the first wireless device.The processing circuitry is further configured to determine a schedulingscheme for the D2D communication based on at least the first uplinktiming difference of the first wireless device, which first uplinktiming difference is the difference between the uplink timing of thefirst wireless device to the source network node and the uplink timingof the first wireless device to the target network node.

According to a fifth aspect of embodiments herein, the object isachieved by a method performed by a source network node for handling aD2D communication between a first wireless device and a second wirelessdevice during handover of the first wireless device from the sourcenetwork node to a target network node in a wireless telecommunicationsnetwork. The source network node transmits an indication to interruptthe D2D communication to at least the second wireless device before thehandover is initiated. Then, after completing the handover, the sourcenetwork node determines a scheduling scheme for the D2D communicationbased on at least first uplink timing difference of the first wirelessdevice, which first uplink timing difference is the difference betweenthe uplink timing of the first wireless device to the source networknode and the uplink timing of the first wireless device to the targetnetwork node.

According to a sixth aspect of embodiments herein, the object isachieved by a source network node for handling a D2D communicationbetween a first wireless device and a second wireless device duringhandover of the first wireless device from the source network node to atarget network node in a wireless telecommunications network. The sourcenetwork node comprising processing circuitry configured to transmit anindication to interrupt the D2D communication to at least the secondwireless device before the handover is initiated. The processingcircuitry is further configured to determine, after completing thehandover, a scheduling scheme for the D2D communication based on atleast a first uplink timing difference of the first wireless device,which first uplink timing difference is the difference between theuplink timing of the first wireless device to the source network nodeand the uplink timing of the first wireless device to the target networknode.

By having wireless devices that are engaged in D2D communicationproviding, to a network node, uplink timing differences between a sourcenetwork node and the tar network node when performing a handover fromthe source network node to the target network node, the network nodesinvolved in controlling the D2D communication may determine a schedulingscheme for the D2D communication to be used after the handover iscompleted. That is, based on the uplink timing differences, the networknodes may reach an agreement on the time locations that are to be usedfor the scheduling of the D2D communication. This scheduling scheme willthus efficiently avoid collisions when having a split network controlpoint, i.e. two network nodes controlling the D2D communication, whichis scheduling resources for the cellular and D2D links. Hence, a way ofhandling a D2D communication during handover of wireless device in awireless communications network is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the embodiments will become readily apparelto those skilled in the art by the following detailed description ofexemplary embodiments thereof with reference to the accompanyingdrawings, wherein:

FIG. 1 is a schematic block diagram illustrating embodiments in awireless communications network.

FIG. 2A-2B are schematic block diagrams illustrating a first D2Dhandover scenario according to some embodiments.

FIG. 3 is a schematic signaling diagram depicting signaling according tosome embodiments in the first D2D handover scenario of FIG. 2.

FIG. 4A-4B are schematic block diagrams illustrating a second D2Dhandover scenario according to some embodiments.

FIG. 5 is a schematic signaling diagram depicting signaling according tosome embodiments in the second D2D handover scenario of FIG. 4.

FIG. 6A-6B are schematic block diagrams illustrating a third D2Dhandover scenario according to some embodiments.

FIG. 7 is a schematic signaling diagram depicting signaling according tosome embodiments in the third D2D handover scenario of FIG. 6.

FIG. 8 is a flowchart depicting embodiments of a method in wirelessdevice.

FIG. 9 is a flowchart depicting embodiments of a method in targetnetwork node.

FIG. 10 is a flowchart depicting embodiments of a method in sourcenetwork node.

FIG. 11 is a block diagram depicting embodiments of a wireless device.

FIG. 12 is a block diagram depicting embodiments of a target networknode.

FIG. 13 is a block diagram depicting embodiments of a source networknode.

DETAILED DESCRIPTION

The figures are schematic and simplified for clarity, and they merelyshow details which are essential to the understanding of the embodimentspresented herein, while other details have been left out. Throughout,the same reference numerals are used for identical or correspondingparts or steps.

FIG. 1 depicts a wireless telecommunications network 100 in whichembodiments herein ay be implemented. In some embodiments the wirelesstelecommunications network 100 may be a wireless telecommunicationnetwork such as an LTE (e.g. LTE LTE TDD, LTE HD-FDD), WCDMA, UTRA TDD,GSM network, GERAN network, enhanced data rate for GSM evolution (EDGE)network, network comprising of any combination of RATs such as e.g.Multi-Standard Radio (MSR) base stations, multi-RAT base stations etc.,any 3GPP cellular network, Wimax, or any cellular network or system.

The wireless telecommunications system 100 comprises a first radionetwork node 110 which is a radio base station and may therefore also bereferred to as a radio base station or base station. The network node110 serves a first cell 115. The network node 110 may in this examplee.g. be an eNB, eNodeB, or a Home Node B, a Home eNode B, femto BaseStation (BS), pico BS or any other network unit capable to serve awireless device or a machine type communication device in a wirelesstelecommunications system, e.g. a device such as a cluster head.

A first wireless device 121 is located within the first cell 115. Thewireless device 121 is configured to communicate within the wirelesscommunications system 100 via the radio network node 110 over a radiolink 130 when present in the first cell 115 served by the radio networknode 110. The first wireless device 121 is capable of communicating withother wireless devices, such as, a second wireless device 122 to bedescribed below using wireless D2D communication, over a D2D link 140(dashed arrow in FIG. 1).

In this example, a second wireless device 122 is also located within thefirst cell 115. However, in other embodiments, the second wirelessdevice 122 may be located in another cell, such as, e.g. second cell 115served by another second radio network node 111, which is adjacent tothe first cell 115. The second wireless device is configured tocommunicate within the wireless communications system 100 via the firstradio network node 110 over a radio link such as e.g. a radio link 150when present in the first cell 115 served by the base station 110. Thesecond wireless device 122 is capable of communicating with otherwireless devices such as the first wireless device 121 using wirelessD2D communication over the D2D link 140.

It should be noted that the first wireless device 121 and the secondwireless device 122 may e.g. be wireless devices, e.g. be mobileterminals or wireless terminals, mobile phones, computers such as e.g.laptops, Personal Digital Assistants (PDAs) or tablet computers withwireless capability, Machine to Machine (M2M) devices or any other radionetwork units capable to communicate over a radio link in acommunications network.

It should also be noted that a large number of wireless devices may belocated in the communications network 100. The first and second wirelessdevice 121, 122 may be seen as one D2D pair of wireless devices amongmany more D2D pairs of wireless devices located in the communicationsnetwork 100.

However, when one of the wireless devices, e.g. the first wirelessdevice 121, is moving out of the cellular coverage of the first cell 115and into the cellular coverage of another cell, e.g. the second cell115, the first radio network node 110 may no longer be able to controlthe scheduling of the D2D communication if a handover is subsequentlyperformed of the first wireless device 121 to the second radio networknode 111.

Thus, in this case, the network control point of the D2D communicationbetween the wireless devices would need to be split between the firstand the second radio network nodes 110, 111. Here, avoiding collisions,i.e. where the first radio network node schedules for the D2Dcommunication and the second radio network node schedules for cellularcommunication, when having a split network control point schedulingresources for the cellular and D2D becomes a problem. This problem willappear for both synchronized and unsynchronized neighboring cells, Forthe unsynchronized case, there is also a problem in that the cell timingis different for the two cells and unknown to the D2D pair of wirelessdevices, i.e. the D2D pair of wireless devices is onetransmitting/receiving pair of devices whereby the D2D communicationbetween these wireless devices should be synchronized.

This issue is addressed by embodiments described herein by having thewireless devices 121, 122 that are engaged in a D2D communicationproviding uplink timing differences between the uplink timing to asource network node, i.e. the network node of their respective currentcell, and the uplink timing to a target network node, i.e. the networknode of the cell they are moving into, when performing a handover fromthe source network node to the target network node. Thus, the networknodes involved in controlling the D2D communication may determine ascheduling scheme for the D2D communication to be used after thehandover is completed. That is, based on the uplink timing differences,the network nodes may reach an agreement on the time locations that areto be used for the scheduling of the D2D communication. This schedulingscheme will thus efficiently avoid collisions when having a splitnetwork control point that are scheduling resources for the cellular andD2D link. Hence, a way of handling a D2D communication during handoverof wireless device in a wireless communications network is provided.

Below, three different D2D handover scenarios are described in moredetail with reference to FIGS. 2-7, which illustrate the differenthandover situations that are handled by the embodiments presented hereinfor D2D communications. Thereafter, the embodiments are also furtherdescribed in reference to FIGS. 8-13.

FIGS. 2A-2B shows a first D2D handover scenario according to soembodiments. In FIG. 2A, the first wireless device 121 is engaged in aD2D communication with the second wireless device 122 over the D2D link140. In this first D2D handover scenario, the first wireless device 121then starts to move out of the cellular coverage of its current cell,i.e. the first cell 115 served by the first network node 110, and intothe cellular coverage of the second cell 115 served by the secondnetwork node 111 (as shown by the dashed, double lined arrow). The firstnetwork node 110 may in this scenario be referred to as the sourcenetwork node, and the second network node 111 referred to as the targetnetwork node. This may trigger the signaling of embodiments described indetail below with reference to FIG. 3.

As shown in FIG. 2B, once this signaling of FIG. 3 has been completed,the first wireless 121 will have performed a handover from the firstnetwork node 110 to the second network node 111. This means that thefirst wireless device 121 is now located in the second cell 115 and isbeing served by the second network node 111. As a consequence of thesignaling of FIG. 3, the first wireless device 121 will also still beengaged in the D2D communication with the second wireless device 122over the D2D link 140, where the second wireless device 122 is stilllocated in the first cell 115 and being served by the first network node110.

FIG. 3 shows signaling of some embodiments triggered by the first D2Dhandover scenario shown in FIG. 2A. The signaling may be described bythree main signaling blocks: a D2D handover preparation stage 301, a D2Dhandover execution stage 302, and a D2D scheduling stage 303.

As shown in FIG. 3, prior to the signaling, the first wireless device121 is engaged in a D2D communication with the second wireless device122 over a D2D link. The first and second wireless device 121, 122 haveeach also an established cellular link with the first network node 110,i.e. the source network node 110. In this example, the source networknode 110 and the target network node 111 are not synchronized with eachother.

In the D2D handover preparation stage 301, a conventional wirelessdevice measurement report by the first wireless device 121 may triggerthe handover procedure for both the source network node 110 and thetarget network node 111.

Action 301 a. The first wireless device 121 may transmit a measurementreport to the source network node 110. The measurement report may bebased on the determined information elements, MeasConfig andReportConfig Radio Resource Control, RRC, Information Element, IE).These IEs may have been transmitted to the first and second wirelessdevice 121, 122 by the source network node 110 beforehand.

Upon receiving the measurement report from the first wireless device121, the source network node 110 is notified that the first wirelessdevice 121, which is engaged in a D2D communication with the secondwireless device 122, in ends to change serving cell, i.e. move out ofthe coverage area of the source network node 110 and into the coveragearea of the target network node 111.

Action 301 b. In response to the measurement report, the source networknode 110 sends a handover request to the target network node 11 l via anX2 interface. Here, the source network node 110 may add, in the handoverrequest, the information that the first wireless device 121 is aD2D-capable wireless device and that there is an ongoing D2Dcommunication related to the first wireless device 121. This allows thetarget network node 111 to decide whether to accept the first wirelessdevice 121 based on the target network node's 111 capabilities, e.g.whether it can handle a D2D communication or not, and current networkload.

Action 301 c. In response to the handover request, the target networknode 111 may send a handover request acknowledgement, ACK, to the sourcenetwork node 110. This handover request ACK indicates to the sourcenetwork node 110 that the target network node 111 is ready to accept thehandover of the first wireless device 121. In some embodiments, the IEMobilityCortrolInfo may be piggybacked on this signaling. This wouldotherwise be sent to the first wireless device 121 later for access tothe target network node 111.

Next, the D2D handover execution stage 302, by command from the sourcenetwork node 110, the first wireless device 121 may switch servingnetwork node to the target network node 111. In this stage, according tosome embodiments, the main task of the first wireless device 121 is tomeasure and report the uplink timing difference between the sourcenetwork node 110 and the target network node 111 during the handover.The uplink timing difference is here the difference between the uplinktiming to the source network node 110 and the uplink timing to thetarget network node 111.

Action 302 a. The source network node 110 may here transmit a messageindicating to the first and second wireless device 121, 122 that the D2Dcommunication should be interrupted before the handover is initiated. Inresponse o receiving this message, the first and second wireless device121, 122 may interrupt or temporarily pause the D2D communicationbetween the first and second wireless device 121, 122.

However, it should be noted that if the D2D communication is based ondynamic scheduling, which is performed on a short-time-scale, such as,e.g. per Transmission-Time-Interval, i.e. 1 ms, there is here no needfor an independent signaling to stop the D2D communication. The sourcenetwork node 110 may simply stop scheduling the D2D communication. Onthe other hand, if the D2D communication is based on Semi-PersistentScheduling, SPS, which is performed on a large-time-scale, such as, e.g.about 100-500 ms, it may be necessary to temporarily interrupt ortemporarily pause the SPS.

In some embodiments, the message may be a Semi-Persistent SchedulingRelease on PDCCH message. This may be sent to and received by the firstand second wireless device 121, 122 in order to release the resources,e.g. by using a shared Radio Network Temporary Identifier, RNTI, for theD2D communication, D2D_RNTI.

Action 302 b. In this action, the source network node 110 may transmit amessage to the first wireless device 121 indicating that the firstwireless device 121 is to switch serving network node from the sourcenetwork node 110 to the target network node 111, i.e. switch servingcell. Related information to perform the switch may be comprised in themessage, e.g. as a MobilityControlInfo IE, received by the sourcenetwork node 110 from the target network node 111. According to someembodiments, this message may also indicate the first wireless device121 to perform measurements of the uplink timing to the source andtarget network nodes 110, 111, and report the uplink timing differencebetween the source and target network nodes 110, 111. The message maye.g. be a RRC connection Reconfiguration message.

Action 302 c. Through a contention-free or contention-based RandomAccess CHannel, RACH, procedure with the target network node 111, thefirst wireless device 121 may acquire the uplink timing of the targetnetwork node 111 via a Random Access Response, RAR, message from thetarget network node 111. The first wireless device 121 may then comparethe uplink timing of the target network node 111 with the uplink timingof the source network node 110, and thus determine the uplink timingdifference between the source and target network nodes 110, 111.

It should be noted that the content of this uplink timing difference canbe various. For coordination of the scheduling between the source andtarget network node 110, 111, it may be enough to acquire the uplinktiming difference in the order of number of subframes.

However, e.g. for inter-cell peer discovery or for interferencecoordination, the accuracy of the uplink timing difference may have tobe at a level of more accurate granularity, e.g. at a level of symbol,sample, etc. Thus, the embodiments herein should not be construed asbeing limited to a specific quantification scheme of the uplink timingdifference.

Action 302 d. In this action, the first wireless device 121 may send amessage indicating a successful handover to the first wireless device121 to the target network node 111. This message may also comprise thedetermined uplink timing difference between the source and targetnetwork nodes 110, 111, and thus the determined uplink timing differencemay be reported. to the target network node 111. The message may e.g. bea RRC connection Reconfiguration Complete message.

In the D2D scheduling stage 303, the source and target network nodes110, 111 may negotiate the scheduling scheme for the D2D communication,i.e. in which subframes transmission resources should be allocated forthe D2D communication, based on e.g. the time partition between currentcellular and D2D communication mode and the cell timing of the sourceand target network nodes 110, 111, respectively. The resulting D2Dscheduling scheme is then sent to both the first and second wirelessdevices 121, 122 to re-start D2D communication again. It should also benoted that this procedure is applicable for both synchronized andunsynchronized cells.

Action 303 a-303 b. In these actions, the source and target networknodes 110, 111 may send inter-cell coordination messages via an X2interface between each other. The messages may e.g be a SchedulingCoordination Request messages and Scheduling Coordination Request ACKmessages. The source and target network nodes 110, 111 needs to reach anagreement about the time locations of the subframes to be used for theD2D communication. Otherwise, the source network node 110 may schedule asubframe for the D2D communication while the target network node 11schedules the same subframe for cellular communication, which wouldcause a scheduling collision.

It should also be noted that the content of the X2 signaling between thesource and target network nodes 110, 111 may be various. For example, itcould be a numerical or binary value for each subframe, such as, e.g. 0for a cellular subframe, 1 for a D2D subframe. According to anotherexample, more information may be comprised therein, e.g. value 2 for anegotiable subframe. This may be advantageous since the source networknode 110 may have its own preference on the subframe allocation for theD2D communication.

Furthermore, the procedure of this negotiation may be various. It maye.g be triggered by the source network node 110 or the target networknode 11, and accepted/rejected by the other. Other, negotiationprocedures can also be envisioned.

Action 303 c-303 d. When a D2D scheduling scheme has been agreed upon bythe source and target network nodes 110, 111, source and target networknodes 110, 111 may send the D2D scheduling scheme to the second andfirst wireless device 121, 122, respectively. This may be performed viaan SPS procedure, e.g. SPS activation PDDCH messages may be used by thesource and target network nodes 110, 111.

In response to receiving the D2D scheduling scheme, the first and secondwireless device 121, 122 may re-start the D2D communication based on thereceived D2D scheduling scheme. Also, subsequently, the first and secondwireless device 121, 122 may then, based on the TDD configuration of theD2D bearer, decide on further matters of the D2D communication, such as,e.g. resource location, HARQ timing and etc.

It should be noted that the term “re-started” used throughout theembodiments herein is to be interpreted as continuing the D2Dcommunication from the point in time where it was interrupted.

FIGS. 4A-4B shows a second D2D handover scenario according to someembodiments. In FIG. 4A, the first wireless device 121 is engaged in aD2D communication with the second wireless device 122 over the D2D link140. The first wireless device 122 is here located in a different cellthan the second wireless device 122, i.e. in second cell 116 served bythe second network node 111. This situation may occur, for example, as aconsequence of the first scenario described above.

In this second D2D handover scenario, the first wireless device 121 thenstarts to move out of the cellular coverage of its current cell, i.e.the second cell 116 served by the second network node 111, and into thecellular coverage of the first cell 115 served by the first network node110 (as shown by the dashed, double lined arrow). This means that thefirst wireless device 121 moves into the cell of the second wirelessdevice 122.

The second network node 111 may in this scenario be referred to as thesource network node, and the first network node 110 referred to as thetarget network node. This may trigger the signaling of embodimentsdescribed in detail below with reference to FIG. 5.

As shown in FIG. 4B, once this signaling of FIG. 5 has been completed,the first wireless 121 will have performed a handover from the secondnetwork node 111 to the first network node 110. This means that thefirst wireless device 121 is then located in the first cell 115 and isbeing served by the first network node 110. As a consequence of thesignaling of FIG. 5, the first wireless device 121 will also havemaintained the D2D communication with the second wireless device 122over the D2D link 140. Since both the first and the second wirelessdevice 121, 122 are now located in the same cell, i.e. the first cell115, the first network node 110 will now form a single network controlpoint of the D2D communication and may schedule the D2D communication.

FIG. 5 shows signaling of some embodiments triggered by the second D2Dhandover scenario shown in FIG. 4A. The signaling may be described bytwo main signaling blocks: a D2D handover preparation stage 501 and aD2D handover stage 502.

As shown in FIG. 5, prior to the signaling, the first wireless device121 is engaged in a D2D communication with the second wireless device122 over a D2D link within two different cells. The first and secondwireless device 121, 122 have each also an established cellular linkwith the second and first network node 111, 110, respectively, i.e. thesource and target network node. In this example, the source network node111 and the target network node 110 are not synchronized with eachother.

In the D2D handover preparation stage 501, a conventional wirelessdevice measurement report by the first wireless device 121 may triggerthe handover procedure for both the source network node 111 and thetarget network node 110.

Action 501 a. The first wireless device 121 transmits a measurementreport to the source network node 111. Upon receiving the measurementreport from the first wireless device 121, the source network node 111is notified that the first wireless device 121, which is engaged in aD2D communication with the second wireless device 122, intends to changeserving cell, i.e. move out of the coverage area of the source networknode 111 and into the coverage area of the target network node 110.

Action 501 b. In response to the measurement report, the source networknode 111 sends a handover request to the target network node 110 via anX2 interface. Here, the source network node 111 may add, in the handoverrequest, the information that first wireless device 121 is a D2D-capablewireless device.

Action 501 c. In response to the handover request, the target networknode 110 may send a handover request acknowledgement, ACK, to the sourcenetwork node 111. This handover request ACK indicates to the sourcenetwork node 111 that the target network node 110 is ready to accept thehandover of the first wireless device 121.

Next, in the D2D handover execution stage 502, by command from thesource network node 111, the first wireless device 121 may switchserving network node to the target network node 110. In this secondscenario, however, there is no need for the first wireless device 121 tomeasure and report any uplink timing difference since it moves into thesame cell as the second wireless device 122 and into the control of thesame network node. This means that there is no longer any uplink timingdifference because of both wireless devices are being served by the samenetwork node.

Action 502 a. The source network node 111 may transmit a messageindicating to the first wireless device 121 that the D2D communicationshould be interrupted before the handover is initiated. In response toreceiving this message, the first wireless device 121 may interrupt ortemporarily pause the D2D communication between the first and secondwireless device 121, 122.

Action 502 b. The target network node 110 may transmit a messageindicating the second wireless device 122 that the D2D communicationshould be interrupted before the handover is initiated. In response toreceiving this message, the second wireless device 122 may interrupt ortemporarily pause the D2D communication between the first and secondwireless device 121, 122.

Action 502 c. In this action, the source network node 111 may transmit amessage to the first wireless device 121 indicating that the firstwireless device 121 is to switch serving network node from the sourcenetwork node 111 to the target network node 110, i.e. switch servingcell. The message may e.g. be a RRC connection Reconfiguration message.

Action 502 d. In this action, the first wireless device 121 may performa contention-free or contention-based Random Access CHannel, RACH,procedure with the target network node 110 without the need to acquireany uplink timing.

Action 502 e. In this action, the first wireless device 121 may send amessage indicating a successful handover of the first wireless s device121 to the target network node 110. The message may e.g. be a RRCconnection Reconfiguration Complete message.

Action 502 f. Now, the target network node 110 may determine thescheduling scheme for the D2D communication. The resulting D2Dscheduling scheme is then sent to the first and second wireless devices121, 122 to re-start D2D communication again. This may be performed viaa SPS procedure. Then based on the TDD configuration of the D2D bearer,the first and second wireless devices 121, 122 may decide the resourcelocation, HARQ timing, etc. for the D2D communication.

FIGS. 6A-6B shows a third D2D handover scenario according to someembodiments, in FIG. 6A, the first wireless dev is engaged in a D2Dcommunication the second wireless device 122 over the D2D link 140. Thefirst wireless device 121 is also in this case located in a differentcell than the second wireless device 122, i.e. in second cell 116 servedby the second network node 110. This situation may for example occur asa consequence of the first scenario described above.

In this third D2D handover scenario, the first wireless device 121 thenstarts to move out of the cellular coverage of its current cell, i.e.the second cell 116 served by the second network node 111, and into thecellular coverage of a third cell 117 served by a third network node 112(as shown by the dashed, double lined arrow). The second network node111 may in this scenario be referred to as the source network node, andthe third network node 112 referred to as the target network node. Thismay trigger the signaling of embodiments described in detail below withreference to FIG. 7.

As shown in FIG. 6B, once this signaling of FIG. 7 has been completed,the first wireless 121 will have performed a handover from the secondnetwork node 111 to the third network node 111.

This means that the first wireless device 121 is then located in thethird cell 117 and is being served by the third network node 112. As aconsequence of the signaling of FIG. 7, the first wireless device 121will also have maintained the D2D communication with the second wirelessdevice 122 over the D2D link 140, where the second wireless device 122is still located in the first cell 115 and being served by the firstnetwork node 110.

FIG. 7 shows signaling of some embodiments triggered by the third D2Dhandover scenario shown in FIG. 6A. The signaling may be described bythree main signaling blocks: a D2D handover preparation stage 601, a D2Dhandover execution stage 602, and a D2D scheduling stage 603.

As shown in FIG. 7, prior to the signaling, the first wireless device121 is engaged in a D2D communication with the second wireless device122 over a D2D link between two different cells, i.e. the second andfirst cell 116, 115, respectively. The first and second wireless device121, 122 have each also an established cellular link with the second andfirst network node 111, 110, respectively. In this example, the networknodes involved, i.e. the first, second and third network node, are notsynchronized with each other.

In the D2D handover preparation stage 701, a conventional wirelessdevice measurement report by the first wireless device 121 may triggerthe handover procedure for the source network node 111, the targetnetwork node 112 and the first network node 110.

Action 701 a. The first wireless device 121 may transmit a measurementreport to the source network node 111, Upon receiving the measurementreport from the first wireless device 121, the source network node 111is notified that the first wireless device 121, which is engaged in aD2D communication with the second wireless device 122 in cell 115,intends to change serving cell, i.e. move out of the coverage area ofthe source network node 111 and into the coverage area of the targetnetwork node 112.

Action 701 b. In response to the measurement report, the source networknode 111 sends a handover request to the target network node 112 via anX2 interface. Here, the source network node 111 may add, in the handoverrequest, the information that first wireless device 121 is a D2D-capablewireless device and that there is an ongoing D2D communication relatedto the first wireless device 121. This allows the target network node112 to decide whether to accept the first wireless device 121 based onthe target network node's 112 capabilities, e.g. whether it can handle aD2D communication or not, and current network load.

Action 701 c. In response to the handover request, the target networknode 112 may send a handover request acknowledgement, ACK, to the sourcenetwork node 111. This handover request ACK indicates to the sourcenetwork node 111 that the target network node 112 is ready to accept thehandover of the first wireless device 121. In some embodiments, the IEMobilityControlInfo may be piggybacked on this signaling. This wouldotherwise be sent to the first wireless device 121 later for access tothe target network node 112.

Action 701 d. Further, in this action, the source network node 111 mayalso send a message to the first network node 110 indicating a temporaryrelease of the D2D resources for the D2D communication, i.e. indicatingto the first network node 110 that the D2D communication should beinterrupted or temporarily paused. This is performed before the handoverof the first wireless device 121 is initiated.

Next, in the D2D handover execution stage 702, by command from thesource network node 111, the first wireless device 121 may switchserving network node to the target network node 112. In this stage,according to some embodiments, the main task of the first wirelessdevice 121 is to measure and report the uplink timing difference betweenthe source network node 111 and the target network node 112 during thehandover. The uplink timing difference is here the difference betweenthe uplink timing to the source network node 111 and the uplink timingto the target network node 112.

Action 702 a. In response to the message from the source network node111 in Action 701 d, the first network node 110 may send a messageindicating to the second wireless device 122 that the D2D communicationshould be interrupted before the handover is initiated. In response toreceiving this message, the second wireless device 122 may interrupt ortemporarily pause the D2D communication between the first and secondwireless device 121, 122.

Action 702 b. The source network node 111 may transmit a messageindicating to the first wireless device 121 that the D2D communicationshould be interrupted before the handover is initiated. In response toreceiving this message, the first wireless device 121 may interrupt ortemporarily pause the D2D communication between the first and secondwireless device 121, 122. It should be noted that the D2D communication-. ay be interrupted by the second wireless device 122 as in Action 702a, by the first wireless device 121 as described in this Action 702 b,or by both the first and second wireless device 121, 122.

Action 702 c. In this action, the network node 111 may transmit amessage to the first wireless device 121 indicating that the firstwireless device 121 is to switch serving network node from the sourcenetwork node 111 to the target network node 112, i.e. switch servingcell. Related information to perform the switch may be comprised in themessage, e.g. as a MobilityControlInfo IE, received by the sourcenetwork node 111 from the target network node 112, e.g. via X2signaling. According to some embodiments, this message may also indicatethe first wireless device 121 to perform measurements of the uplinktiming to the source and target network nodes 111, 112, and report theuplink timing difference between the source and target network nodes111, 112. The message may e.g. be a RRC connection Reconfigurationmessage.

Action 702 d. Through a contention-free or contention-based RandomAccess CHannel, RACH, procedure with the target network node 112, thefirst wireless device 121 may acquire the uplink timing of the targetnetwork node 112 via a Random Access Response, RAR, message from thetarget network node 112. The first wireless device 121 may then comparethe uplink timing of the target network node 112 with the uplink timingof the source network node 111, and thus determine the uplink timingdifference between the source and target network nodes 111, 112.

It should be noted that the content of this uplink timing difference canbe various. For coordination of the scheduling between the source andthe target network nodes 111, 112, it may be enough to acquire theuplink timing difference in the order of number of subframes.

Action 702 e. In this action, the first wireless device 121 may send amessage indicating a successful handover of the first wireless device121 to the target network node 112. This message may also comprise thedetermined uplink timing difference between the source and network nodes111, 112, and thus the determined uplink timing difference may bereported. to the target network node 112. The message may e.g. be a RRCconnection Reconfiguration Complete message.

In the D2D scheduling stage 703, the target network node 112 and thefirst network node 110 may negotiate the scheduling scheme for the D2Dcommunication, i.e. in which subframes transmission resources should beallocated for the D2D communication. This may be based on e.g. the timepartition between current cellular and D2D communication mode and thecell timing of the target and first network node 112, 110, respectively.

This negotiation rimy be performed via source network node 111, whichmay act as a bridge between the target network node 112 and the firstnetwork node 110. The resulting D2D scheduling scheme is then sent toboth the first and second wireless devices 121, 122 to re-start D2Dcommunication again by the respective network nodes. It should also benoted that this procedure is applicable for both synchronized andunsynchronized cells.

Action 703 a-703 b. In these actions, the target and first network node112, 110 may send inter-cell coordination messages via an X2 interfacebetween each other. This is performed via the source network node 111,which receives and sends the messages onwards to respective networknode. The messages may e.g be a Scheduling Coordination Request messagesand Scheduling Coordination Request ACK messages.

Here, it should be noted that here the target network node 112 may onlybe aware of the uplink timing difference between the source and thetarget network node 111, 112, but is blind to the uplink timing of thefirst network node 110, However, the source network node 111 is aware ofthe uplink timing difference between itself and the first network node110. Hence, by conveying this information to the target network node112, the target network node may determine the uplink timing differencebetween the target and the first network node 112, 110.

The target and first network node 112, 110 needs to reach an agreementon the time locations of the sublimates to be used for the. D2Dcommunication. Otherwise, a D2D scheduling collision may occur aspreviously described.

It should also be noted that the content of the X2 signaling between thetarget and first network node 112, 110 may be various. For example, itcould be a binary value for each subframe, such as, 0 for a cellularsubframe, 1 for a D2D subframe. According to another example, moreinformation may be comprised therein, e.g. a value 2 for a negotiablesubframe.

Furthermore, the procedure of this negotiation may be various. It maye.g be triggered by the target network node 112 or the first networknode 110, and accepted or rejected by the other. According to anotherexample, there may be a pre-negotiation procedure between the source andthe target network node for acquiring the uplink timing differences, orsome negotiation procedures between first network node 110 and thesource network node 111 may be implemented. Further negotiationprocedures may also be envisioned with the same result.

Action 703 c-703 d. When a D2D scheduling scheme has been agreed upon bythe target and first network node 112, 110, the target and first networknode 112, 110 may send the D2D scheduling scheme to the first and secondwireless device 121, 122, respectively. This may be performed via an SPSprocedure, e.g. SPS activation PDDCH messages may be used by the targetand first network node 112, 110.

In response to receiving the D2D scheduling scheme, the first and secondwireless device 121, 122 may re-start the D2D communication based on thereceived D2D scheduling scheme. Also, subsequently, the first and secondwireless device 121, 122 may then, based on the TDD configuration of theD2D bearer, decide on further matters of the D2D communication, such as,e.g. resource location, HARQ timing and etc.

Example of embodiments of a method performed by a first wireless device121 for handling a D2D communication with a second wireless device 122during handover of the first wireless device 121 from a source networknode 110, Ill to a target network node 111, 112 in a wirelesstelecommunications network 100, will now be described with reference toa flowchart depicted in FIG. 8.

Here, the method is discussed seen from the perspective of the firstwireless device 121.

The method may comprise the following actions, which actions may takenin any suitable order.

Action 801. In this action, the first wireless device 121 interrupts theD2D communication. This may be performed in response to receiving anindication to interrupt the D2D communication from a source network nodbefore the handover is initiated. For example, as described above inAction 302 a, 502 a and 702 b.

Action 802. In this action, the first wireless device 121 determines afirst uplink timing difference as the difference between the uplinktiming to the source network node and the uplink timing to the targetnetwork node.

In some embodiments, the first wireless device 121 may determine theuplink timing to the target network node as part of a random accessprocedure being performed between the first wireless device 121 and thetarget network node during the handover. The uplink timing differencesmay e.g. be determined in the order of number of subframes.

Action 803. Based on the first uplink timing difference, the firstwireless device 121 reconfigures the D2D communication.

In some embodiments, this may be performed by the first wireless device121 by transmitting the determined first uplink timing difference to thetarget network node after the handover has been completed. For example,as described above in Action 302 d, 502 e and 702 e.

In some embodiments, this may be accompanied by the first wirelessdevice 121 also transmitting a second uplink timing difference to thetarget network node. This may occur when a second uplink timingdifference has been determined by the first wireless device 121 for theD2D communication, which second uplink timing difference is thedifference between the uplink timing to the source network node and theuplink timing to a third network node. For example, as described abovein Action 702 e.

Then, in response, the first wireless device 121 may receive ascheduling scheme for the D2D communication from the target networknode. The scheduling scheme here indicating time locations of subframesin which transmission resources may be allocated for the D2Dcommunication. For example. as described above in Action 303 d, 502 fand 703 d.

Action 804. In this action, the first wireless device 121 restarts theD2D communication as reconfigured in Action 803.

Example of embodiments of a method performed by a target network nodefor handling a D2D communication between a first wireless device 121 anda second wireless device 122 during handover of the first wirelessdevice 121 to the target network node from a source network node in awireless telecommunications network 100, will now be described withreference to a flowchart depicted in FIG. 9.

Here, the method is discussed seen from the perspective of the targetnetwork node. The target network node may here be the second radionetwork node 111 in the first D2D handover scenario shown and describedabove with reference to FIGS. 2-3, the first radio network node 110 inthe second D2D handover scenario shown and described above withreference to FIGS. 4-5, or the third radio network node 112 in the thirdD2D handover scenario shown and described above with reference to FIGS.6-7.

The method may comprise the following actions, which actions may betaken in any suitable order.

Action 901. In this action, the target network node, after completingthe handover, receives at least a first uplink timing difference of thefirst wireless device 121 from the first wireless device 121. Forexample, as described above in Action 302 d, 502 e and 702 e. In someembodiments, the target network node may also receive a second uplinktiming difference of the first wireless device 121 from the firstwireless device 121. For example, as described above in Action 702 e.

Action 902. In this action, the target network node determines ascheduling scheme for the D2D communication based on at least the firstuplink timing difference of the first wireless device 121. The firstuplink timing difference is the difference between the uplink timing ofthe first wireless device 121 to the source network node and the uplinktiming of the first wireless device 121 to the target network node.

In some embodiments, this may be performed by the target network node bydetermining, through communications with the source network node over anX2 interface, time locations of subframes in which transmissionresources may be allocated for the D2D communication. For example, asdescribed above in Action 303 a-303 b and Action 703 a-703 b.

In some embodiments, when the target network node has also received asecond uplink timing difference of the first wireless device 121 fromthe first wireless device 121, this may be further performed by thetarget network node also based on the second uplink timing difference ofthe first wireless device 121. The second unlink timing difference ofthe first wireless device 121 may here be the difference between theuplink timing of the first wireless device 121 to the source networknode and the uplink timing of the first wireless device 121 to the thirdnetwork node. For example, as described above in Action 703 a-703 b.

In addition, the determining may also be performed by the target networknode by communicating with the third network node, when the thirdnetwork node is serving the second wireless device 121. For example, asdescribed above in Action 703 a-703 b.

Action 903. In this action, the target network node may transmit thescheduling scheme of the D2D communication to the first wireless device121. For example, as described above in Action 303 d, 502 f and 703 d.

Example of embodiments of a method performed by a source network nodefor handling a D2D communication between a first wireless device 121 anda second wireless device 122 during handover of the first wirelessdevice 121 from the source network node to a target network node in awireless telecommunications network 100, will now be described withreference to a flowchart depicted in FIG. 10.

Here, the method is discussed seen from the perspective of the sourcenetwork node. The source network node may here be the first radionetwork node 110 in the first and second D2D handover scenario shown anddescribed above with reference to FIGS. 2-5, or the second radio networknode 111 in the third D2D handover scenario shown and described abovewith reference to FIGS. 6-7.

The method may comprise the following actions, which actions may betaken in any suitable order.

Action 1001. In this action, the source network node transmits anindication to interrupt the D2D communication to at least the secondwireless device 121, 122 before the handover is initiated. For example,as described above in Action 302 a, 502 a and 702 b.

Action 1002. In this action, the source network node determines, aftercompleting the handover, a scheduling scheme for the D2D communicationbased on at least a first uplink timing difference f the first wirelessdevice, The first uplink timing difference is the difference between theuplink timing of the first wireless device 121 to the source networknode and the uplink timing of the first wireless device 121 to thetarget network node.

In some embodiments, this may be performed by the target network node bydetermining, through communications with the target network node over anX2 interface, time locations of the subframes in which transmissionresources may be allocated for the D2D communication. For example, asdescribed above in Action 303 a-303 b and Action 703 a-703 b.

Action 1003. In this action, the source network node may transmit thescheduling scheme of the D2D communication to the second wireless device122. For example, as described above in Action 303 c and Action 703 c.

To perform the method actions for handling a D2D communication with asecond wireless device 122 during handover of the first wireless device121 from a source network node to a target network node in a wirelesstelecommunications network 100, the first wireless device 121 maycomprise the following arrangement depicted in FIG. 11.

FIG. 11 shows a schematic block diagram of embodiments of the firstwireless device 121.

The first wireless device 121 comprises a processing unit 1110, whichmay also be referred to as processing circuitry or processor. Theprocessing unit 1110 may comprise, or be configured to be connected to,an interrupting/re-starting unit 1101, a determining unit 1102, are-configuring unit 1103, and a transceiving unit 1104.

The interrupting/re-starting unit 1101 may be configured to interruptthe D2D communication. In some embodiments, this may be performed inresponse to receiving an indication to interrupt the D2D communicationfrom a source network node before the handover is initiated. Also, theinterrupting/re-starting unit 1101 may also be configured to restart theD2D communication when it has been reconfigured.

The determining unit 1102 may be configured to determine a first uplinktiming difference as the difference between the uplink timing to thesource network node and the uplink timing to the target network node. Insome embodiments, the transceiving unit 1104 may be configured totransmit the determined first uplink timing difference to the targetnetwork node after the handover has been completed. Then, in someembodiments, the transceiving unit 1104 may receive a scheduling schemefor the D2D communication from the target network node, which schedulingscheme indicates time locations of subframes in which transmissionresources may be allocated for the D2D communication.

In some embodiments, the determining unit 1102 may also be configured toa second uplink timing difference has been determined by the firstwireless device 121 for the D2D communication. In this case, thetransceiving unit 1104 may be further configured to transmit a seconduplink timing difference to the target network node. The second uplinktiming difference is the difference between the uplink timing to thesource network node and the uplink timing to a third network node.

The re-configuring unit 1103 is configured to reconfigure the D2Dcommunication based on the first uplink timing difference.

The embodiments herein for handling a D2D communication in the firstwireless device 121 may be implemented through one or more processors,such as the processing unit 1110 in the first wireless device 121depicted in FIG. 11, together with computer program code for performingthe functions and actions of the embodiments herein. The program codementioned above may also be provided as a computer program product, forinstance in the form of a data carrier carrying computer program codefor performing the embodiments herein when being loaded into the firstwireless device 121. The computer program code may e.g. be provided aspure program code in the wireless device 121 or on a server anddownloaded to the wireless device 121.

The first wireless device 121 may further comprise a memory 1120comprising one or more memory units. The memory 1120 may be arranged tobe used to store data, such as, e.g. information regarding the one ormore intervals at which the energy of the transmission bursts should beincreased to the second energy le to perform the methods herein whenbeing executed in the first wireless device 121.

Those skilled in the art will also appreciate that the processing unit1110 and the memory 1120 described above may refer to a combination ofanalog and digital circuits, and/or one or more processors configuredwith software and/or firmware, e.g. stored in a memory, that whenexecuted by the one or more processors such as the processing unit 1110perform as described above. One or more of these processors, as well asthe other digital hardware, may be included in a singleapplication-specific integrated circuit (ASIC), or several processorsand various digital hardware may be distributed among several separatecomponents, whether individually packaged or assembled into asystem-on-a-chip (SoC).

To perform the method actions for handling a D2D communication between afirst wireless device 121 and a second wireless device 122 duringhandover of the first wireless device 121 to the target network nodefrom a source network node, the target network node may comprise thefollowing arrangement depicted in FIG. 12.

FIG. 12 shows a schematic block diagram of embodiment of the targetnetwork node. The target network node may here be the second radionetwork node 111 in the first D2D handover scenario shown and describedabove with reference to FIGS. 2-3, the first radio network node 110 inthe second D2D handover scenario shown and described above withreference to FIGS. 4-5, or the third radio network node 112 in the thirdD2D handover scenario shown and described above with reference to FIGS.6-7.

The target network node comprises a processing unit 1210, which may alsobe referred to as processing circuitry. The processing unit 1210 in thetarget network node may comprise, or be configured to be connected to, adetermining unit 1201 and a transceiving unit 1202.

The transceiving unit 1202 may be configured to receive least a firstuplink timing difference of the first wireless device 121 from he firstwireless device 121 after completing the handover. In some embodiments,the transceiving unit 1202 may be configured to transmit the schedulingscheme of the D2D communication to the first wireless device 121. Insome embodiments, the transceiving unit 1202 may also be configured toreceive a second uplink timing difference of the first wireless device121 from the first wireless device 121.

The determining unit 1201 is configured to determine a scheduling schemefor the D2D communication based on at least the first uplink timingdifference of the first wireless device 121. The first uplink timingdifference is the difference between the uplink timing of the firstwireless device 121 to the source network node and the uplink timing ofthe first wireless device 121 to the target network node. In someembodiments, the determining unit 1201 may be configured to determinethe scheduling scheme by determining, through communications with thesource network node over an X2 interface, time locations of subframes inwhich transmission resources may be allocated for the D2D communication.

In some embodiments, the determining unit 1201 may also be configured todetermine the scheduling scheme further based on the second uplinktiming difference of the first wireless device 121. The second uplinktiming difference of the first wireless device 121 is here thedifference between the uplink timing of the first wireless device 121 tothe source network node and the uplink timing of the first wirelessdevice 121 to the third network node. In some embodiments, thedetermining unit 1201 may also be configured to determine the schedulingscheme by communicating 7° a third network node, when the third networknode is serving the second wireless device 122.

The embodiments herein for handling a D2D communication a target networknode may be implemented through one or more processors, such as, theprocessing unit 1210 in the target network node depicted in FIG. 12,together with computer program code for performing the functions andactions of the embodiments herein. The program code mentioned above mayalso be provided as a computer program product, for instance in the formof a data carrier carrying computer program code for performing theembodiments herein when being loaded into the target network node. Onesuch carrier may be in the form of a CD ROM disc. It is however feasiblewith other data carriers such as a memory stick. The computer programcode may e.g. be provided as pure program code in the target networknode or on a server and downloaded to target network node.

The target network node may further comprise a memory 1220 comprisingone or more memory units. The memory 1220 may be arranged to be used tostore data, such as, e.g. information regarding the one or moreintervals at which the energy of the transmission bursts should beincreased to the second energy level, to perform the methods herein whenbeing executed in the target network node.

Those skilled in the art will also appreciate that the processing unit1210 and the memory 1220 described above may refer to a combination ofanalog and digital circuits, and/or one or more processors configuredwith software and/or firmware, e.g. stored in a memory, that whenexecuted by the one or more processors such as the processing unit 1210perform as described above. One or more of these processors, as well asthe other digital hardware, may be included in a singleapplication-specific integrated circuit (ASIC), or several processorsand various digital hardware may be distributed among several separatecomponents, whether individually packaged or assembled into asystem-on-a-chip (SoC).

To perform the method actions for handling a D2D communication between afirst wireless device 121 and a second wireless device 122 duringhandover of the first wireless device 121 from a source network node toa target network node, the source network node may comprise thefollowing arrangement depicted in FIG. 13.

FIG. 13 shows a schematic block diagram of embodiments of the sourcenetwork node. The source network node may here be the first radionetwork node 110 in the first and second D2D handover scenario shown anddescribed above with reference to FIGS. 2-5, or the second radio networknode 111 in the third D2D handover scenario shown and described abovewith reference to FIGS. 6-7.

The target network node comprises a processing unit 1310, which may alsobe referred to as processing circuitry. The processing unit 1310 in thetarget network node may comprise, or be configured to be connected to, adetermining unit 1301 and a transceiving unit 1302.

The transceiving unit 1202 may be configured to transmit an indicationto interrupt the D2D communication to at least the second wirelessdevice before the handover is initiated. In some embodiments, thetransceiving unit 1202 may be configured to transmit the schedulingscheme of the D2D communication to the second wireless device 122.

The determining unit 1201 is configured to determine, after the handoveris completed, a scheduling scheme for the D2D communication based on atleast a first uplink timing difference of the first wireless device 121.The first uplink timing difference is the difference between the uplinktiming of the first wireless device 121 to the source network node andthe uplink timing of the first wireless device 121 to the target networknode. In some embodiments, the determining unit 1201 may be configuredto determine the scheduling scheme by determining, throughcommunications with the target network node over an X2 interface, timelocations of the subframes in which transmission resources may beallocated for the D2D communication.

The embodiments herein for handling a D2D communication in a sourcenetwork node may be implemented through one or more processors, such as,the processing unit 1310 in the source network node depicted in FIG. 13,together with computer program code for performing the functions andactions of the embodiments herein. The program code mentioned above mayalso be provided as a computer program product, for instance in the formof a data carrier carrying computer program code for performing theembodiments herein when being loaded into the source network node. Onesuch carrier may be in the form of a CD ROM disc. It is however feasiblewith other data carriers such as a memory stick. The computer programcode may e.g. be provided as pure program code in the source networknode or on a server and downloaded to source network node.

The source network node may further comprise a memory 1320 comprisingone or more memory units. The memory 1320 may be arranged to be used tostore data, such as, e.g. information regarding the one or moreintervals at which the energy of the transmission bursts should beincreased to the second energy level, to perform the methods herein whenbeing executed in the source network node.

Those skilled in the art will also appreciate that the processing unit1310 and the memory 1320 described above may refer to a combination ofanalog and digital circuits, and/or one or more processors configuredwith software and/or firmware, e.g. stored in a memory, that whenexecuted by the one or more processors such as the processing unit 1310perform as described above. One or more of these processors, as well asthe other digital hardware, may be included a singleapplication-specific integrated circuit (AMC), or several processors andvarious digital hardware may be distributed among several separatecomponents, whether individually packaged or assembled into asystem-on-a-chip (SoC).

It should be noted that although the target network node and sourcenetwork node are described as separate entities above for the sake ofclarity, a network node may most commonly be implemented as capable ofbeing both a target network node and a source network node depending onwhich of the first, second or third D2D handover scenario is current thecase. Thus, in this case, the processing unit 1210 and the memory 1220may be the same as the processing unit 1310 and the memory 1320.

The embodiments herein are not limited to the above described preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be construed aslimiting.

What is claimed is:
 1. A method performed by a first wireless device forhandling a device-to-device (D2D) communication with a second wirelessdevice during handover of the first wireless device from a sourcenetwork node to a target network node in a wireless telecommunicationsnetwork, the method comprising: interrupting the D2D communication;determining a first uplink timing difference as the difference betweenthe uplink timing to the source network node and the uplink timing tothe target network node; reconfiguring the D2D communication based onthe first uplink timing difference; and re-starting the D2Dcommunication as reconfigured.
 2. The method according to claim 1,wherein the interrupting is performed in response to receiving anindication to interrupt the D2D communication from a source network nodebefore the handover is initiated.
 3. The method according to claim 1,wherein the uplink timing to the target network node is determined aspart of a random access procedure being performed between the firstwireless device and the target network node during the handover.
 4. Themethod according to claim 1, wherein the reconfiguring further comprisestransmitting the determined first uplink timing difference to the targetnetwork node after the handover has been completed; and receiving ascheduling scheme for the D2D communication from the target networknode, which scheduling scheme indicates time locations of subframes inwhich transmission resources may be allocated for the D2D communication.5. The method according to claim 4, wherein the transmitting furthercomprises transmitting a second uplink timing difference to the targetnetwork node when a second uplink timing difference has been determinedby the first wireless device for the D2D communication, which seconduplink timing difference is the difference between the uplink timing tothe source network node and the uplink timing to a third network node.6. The method according to claim 1, wherein the uplink timingdifferences are determined in the order of number of subframes.
 7. Afirst wireless device for handling a device-to-device (D2D)communication with a second wireless device during handover of the firstwireless device from a source network node to a target network node in awireless telecommunications network, the first wireless devicecomprising processing circuitry configured to: interrupt the D2Dcommunication; determine a first uplink timing difference as thedifference between the uplink timing to the source network node and theuplink timing to the target network node; reconfigure the D2Dcommunication based on the first uplink timing difference; and restartthe D2D communication as reconfigured.
 8. The first wireless deviceaccording to claim 7, wherein the processing circuitry is furtherconfigured to interrupt the D2D communication in response to receivingan indication to interrupt the D2D communication from a source networknode before the handover is initiated.
 9. The first wireless deviceaccording to claim 7, wherein the processing circuitry is furtherconfigured to transmit the determined first uplink timing difference tothe target network node after the handover has been completed, andreceive a scheduling scheme for the D2D communication from the targetnetwork node, which scheduling scheme indicates time locations ofsubframes in which transmission resources may be allocated for the D2Dcommunication.
 10. The first wireless device according to claim 9,wherein the processing circuitry is further configured to transmit asecond uplink timing difference to the target network node when a seconduplink timing difference has been determined by the first wirelessdevice for the D2D communication, which second uplink timing differenceis the difference between the uplink timing to the source network nodeand the uplink timing to a third network node.